U.S. patent application number 10/154327 was filed with the patent office on 2003-01-09 for percussion electrical hand-held power tool with active vibration damping.
Invention is credited to Schaer, Roland, Schmitzer, Harald, Tichy, Stefan.
Application Number | 20030006051 10/154327 |
Document ID | / |
Family ID | 7689046 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030006051 |
Kind Code |
A1 |
Schmitzer, Harald ; et
al. |
January 9, 2003 |
Percussion electrical hand-held power tool with active vibration
damping
Abstract
An electrical hand-held power tool including an arrangement for
actively damping vibrations applied to the tool handle (2) and
arranged between the handle and the hammer mechanism module (3)
with a possibility of a limited axial displacement along the
percussion axis (A) with respect to the hammer mechanism module (3)
and having at least one electromechanical actuator (5a, 5b)
surrounded by an elastic spring (8a, 8b), a sensor for sensing
vibrations acting on the handle (2), and a microprocessor (7) for
dynamically controlling the actuator (5a, 5b) in accordance with
the signal generated by the sensor.
Inventors: |
Schmitzer, Harald;
(Wasserburg, DE) ; Tichy, Stefan; (Frastanz,
AU) ; Schaer, Roland; (Grabs, CH) |
Correspondence
Address: |
DAVID TOREN, ESQ.
SIDLEY, AUSTIN, BROWN & WOOD, LLP
787 SEVENTH AVENUE
NEW YORK
NY
10019-6018
US
|
Family ID: |
7689046 |
Appl. No.: |
10/154327 |
Filed: |
May 22, 2002 |
Current U.S.
Class: |
173/49 ;
173/2 |
Current CPC
Class: |
B25D 17/043 20130101;
B25D 2250/221 20130101; B25D 2211/003 20130101 |
Class at
Publication: |
173/49 ;
173/2 |
International
Class: |
B25D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2001 |
DE |
101 30 088.3 |
Claims
What is claimed is:
1. An electrical hand-held power tool for generating a percussion
load applied to a working tool along a percussion axis (A), the
power tool comprising a handle (2); an oscillating hammer mechanism
module (3); and means for actively damping vibrations applied to
the handle (2) and arranged between the handle and the hammer
mechanism module (3) with a possibility of a limited axial
displacement along the percussion axis (A) with respect to the
hammer mechanism module (3), the vibration damping means comprising
at least one electromechanical actuator (5a, 5b), at least one
elastic spring (8a, 8b) bridging the at least one actuator (5a,
5b), a sensor (11) for sensing vibrations acting on the handle (2),
and a microprocessor (7) for dynamically controlling the at least
one actuator (5a, 5b) for reducing the vibrations acting on the
handle (2) in accordance with a signal generated by the sensor.
2. An electrical hand-held power tool according to claim 1, wherein
the elastic spring (8a, 8b) is non-damped, and the vibration
damping means is supported for a substantially friction-free
limited axial displacement.
3. An electrical hand-held power tool according to claim 1, wherein
the at least one electromechanical actuator (5a, 5b) is arranged
parallel to the percussion axis (A).
4. An electrical hand-held power tool according to claim 1, wherein
the electromechanical actuator (5a, 5b) is formed for operation in
compression and tension regions.
5. An electrical hand-held power tool according to claim 1, wherein
the at least one elastic spring (8a, 8b) is formed as a compression
spring.
6. An electrical hand-held power tool according to claim 5, wherein
the at least one elastic spring (8a, 8b) has a stiffness in a range
from about 30.sup.N/mm to about 50.sup.N/mm.
7. An electrical hand-held power tool according to claim 1, wherein
the at least one elastic spring (8a, 8b) and the at least one
electromechanical actuator (5a, 5b) are coaxially arranged and form
together a damping module.
8. An electrical hand-held power tool according to claim 7, wherein
the at least one elastic spring (8a, 8b) is formed as a
self-supporting helical spring wound about the electromechanical
actuator.
9. An electrical hand-held power tool according to claim 7, wherein
the damping means comprises a further electromechanical actuator
(8a, 8b) and a further elastic spring (8a, 8b) surrounding the
further electromechanical actuator (5a, 5b) and forming therewith a
further damping module spaced from the damping module, which is
formed by the at least one elastic spring and the at least one
electromechanical actuator, along a line extending perpendicular to
the percussion axis (A).
10. An electrical hand-held power tool according to claim 9,
wherein the handle (2) is formed as a U-shaped handle, and each
damping module is associated with a respective leg of the U-shaped
handle.
11. An electrical hand-held power tool according to claim 9,
wherein both damping modules are arranged in a plane in which after
a primary vibration, a second largest secondary vibration
occurs.
12. An electrical hand-held power tool according to claim 9,
wherein the two damping modules are separately controlled by the
microprocessor.
13. An electrical hand-held power tool, according to claim 1,
further comprising a side, additional handle (9) with damped
vibrations.
14. An electrical hand-held power tool according to claim 13,
wherein the additional handle (9) is rigidly connected with the
handle (2) by a handle cup-shaped housing part (10) vibrations of
which are actively damped.
15. An electrical hand-held power tool according to claim 1,
wherein the sensor (11), the microprocessor (7), and the at least
one electromechanical actuator (5a, 5b) form a control circuit for
effecting an active control in a region from 10 Hz to 100 Hz at a
sampling time of less than 1 ms.
16. An electrical hand-held power tool according to claim 1,
wherein the sensor (11), the microprocessor (7), and the at least
one electromechanical actuator (5a, 5b) form a control circuit for
effecting an active control in a region from 2 Hz to 400 Hz at a
sampling time of less than 1 ms.
17. An electrical hand-held power tool according to claim 1,
wherein the sensor (11), the microprocessor (7), and the at least
one electromechanical actuator (5a, 5b) form a control circuit for
effecting an active control in a region from 10 Hz to 100 Hz at a
sampling time of less than 200 us.
18. An electrical hand-held power tool according to claim 1,
wherein the sensor (11), the microprocessor (7), and the at least
one electromechanical actuator (5a, 5b) form a control circuit for
effecting an active control in a region from 2 Hz to 400 Hz at a
sampling time of less than 200 us.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a percussion electrical
hand-held tool, such as a hammer drill or a chisel hammer, with an
active vibration damping of the power tool handle.
[0003] 2. Description of the Prior Act
[0004] As a result of interaction with a workpiece of a working
tool, the handle of the power tool that percussively drives the
working tool is preloaded, as a result of gravitation and a
pressure applied by a user to the handle of the power tool and is
subjected to axial oscillations which should be prevented as much
as possible. These oscillations result from the rebound of the
working tool, the recoil of the hammer mechanism, and the vibration
of the unbalanced eccentric mass. The main or primary oscillation,
which takes place parallel to the percussion axis, should have a
weighted acceleration average that, for protection of the power
tool user, should not exceed 2.5 m/s.sup.2. Therefore, this
vibration limits the power of a percussion electrical hand-held
tool.
[0005] British Publication GB-2154497 discloses an electrical
hand-held tool in which a heavy, oscillation-isolated housing
module, which is supported for a limited axial movement along the
percussion axis with respect to a hammer mechanism module with a
hammer mechanism, is connected with the handle and an auxiliary
handle. The vibrations or oscillations are actively damped by
viscoelastic damping means arranged in the housing module.
[0006] U.S. Pat. No. 5,322,131 discloses a pneumatic percussion
tool which is provided with active, compressed air-controlled
vibration damping means and in which a U-shaped handle is arranged
on a frictionlessly supported, cup-shaped handle housing part
capable of limited axial displacement.
[0007] German Publication DE-35 21 898 discloses a tool in which in
the displacement region of a pressure-loaded handle capable of a
limited axial displacement, an almost constant counter-force, which
is applied to the handle, is electromagnitically generated by
moving coils that act as electromechanical actuators. The movement
of coils is controlled by direct current. As a result of
application of the counter-force to the handle, the handle is
subjected to action of a constant force. For the compensation of
the position of the handle, there are provided sensors which
integrally control the distance between the handle and the tool
housing. The electromechanical actuators must provide for the
application of the entire counter-force to the handle and,
therefore, they should necessarily have relatively large
dimensions, with the voltage source likewise being relatively
large. As a result, the actuators and the voltage source have large
volume and weight which contribute to the total volume and weight
of the tool that can only be increased up to a certain limit.
[0008] German Publication DE 196 46 622 discloses a tool in which a
counter-force acting on a pressure-loaded handle or the position of
the handle is controlled by a microprocessor which emits a control
signal in response to a signal generated by a vibration-sensing
sensor. The control of the counter-force and/or the position is
effected via force-generating moving coils that act as
electromechnical actuators. The vibrations, which are registered by
the sensor, are compensated by directly excited counter-vibrations,
i.e., an active regulation takes place. The electromechnical
actuators are arranged in a row with viscoelastic dampening
elements and, as a result, should provide for application of the
entire counter-force to the handle which likewise results in
increase of the size of the actuators and their voltage source.
[0009] Accordingly, an object of the present invention is to
provide vibration damping means for damping the vibration applied
to the handle of a hand-held percussion power tool and which would
include electromechnical actuators and a voltage source having
sufficiently small dimensions.
SUMMARY OF THE INVENTION
[0010] This and other objects of the present invention, which will
become apparent hereinafter, are achieved by providing a electrical
hand-held power tool for generating a percussion load applied to a
working tool along a percussion axis and including a handle, an
oscillating hammer mechanism module, and an arrangement for
actively damping vibrations applied to the handle, arranged between
the handle and the hammer mechanism module with a possibility of a
limited axial displacement along the percussion axis with respect
to the hammer mechanism module, and having at least one
electromechanical actuator, at least one elastic spring bridging
the at least one actuator, a sensor for sensing vibrations acting
on the handle, and a microprocessor for dynamically controlling the
at least one electromechanical actuator for reducing the vibrations
acting on the handle in accordance with a signal generated by the
sensor.
[0011] As a result of the provision, with respect to the force
flux, of a spring, which is arranged at least partially parallel to
the actuator, the force flux is divided between the spring and the
actuator. Therefore, the electromechanical actuator provides for
application to the handle only a portion of the counter-force
necessary to achieve a balance of forces acting on the handle. As
result, the actuator can have smaller dimensions. Correspondingly,
the power source for the electromechanical actuators likewise can
be made smaller. Preferably, the power source is formed as an
electronic circuit breaker. An optimal control function for
controlling the actuators would include a control which would take
into account, optionally, sensor-measurable parameters such as the
orientation of the power tool, oscillation amplitude of the hammer
mechanism module, average force acting on the handle, and other
parameters specific for the power tool and which are read-out by
the microprocessor from storage means and/or are calculated by the
microprocessor.
[0012] Advantageously, the spring is a high-quality spring and, in
particular, is not viscoelastic. Therefore, the electromechnical
actuators need not overcome any additional passive damping.
Further, advantageously, guide bearings, which provide for the
limited axial movement, are formed so that there is substantially
no friction between the movable parts. E.g., the guide bearings can
be formed as spherical sleeves and as slide bearings.
[0013] Advantageously, the electromechanical actuator is arranged
parallel to the percussion axis. Thereby, the control system can be
made technologically simple, without any additional constructive
measures, for effecting an active vibration damping.
[0014] Advantageously, the electromechanical actuator is so formed
that it operates in both compression and tension regions. As a
result, the actuator should balance only the minimal dynamic force
difference which is directly produced by the vibrations. Therefore,
the electromechnical actuator can have smaller dimensions with
regard to the power to the tool.
[0015] Advantageously, the spring is formed as a compression spring
extending along the percussion axis. Therefore, a substantial
portion of the press-on force applied by the user can be directly
and technologically simply absorbed without any additional
measures. Advantageously, the stiffness of the spring amounts to
from about 30 to about 50 N/mm.
[0016] Advantageously, the elastic spring and the electronic
mechanical actuator are coaxially arranged and form together a
damping module, with the elastic spring being formed as a
self-supporting helical spring wound about the electromechanical
actuator.
[0017] The formation of a damping module of the spring and the
actuator permits to obtain a compact unit and without any bending
or transverse moment.
[0018] Advantageously, there are provided two, spaced from each
other, along a line transverse to the percussion axis, actuators or
damping modules which are, advantageously, are associated,
respectively, with the legs of the handle formed as a U-shaped
handle.
[0019] Advantageously, the two electromechnical actuators or the
two damping modules are arranged in a plane in which after a
primary vibration, a second largest secondary vibration occurs. The
two damping modules are separately controlled by the
microprocessor. As a result of the difference of actions of the two
actuators or damping modules in the plane of the actuators, damping
modules, and due to the spacing between the actuators, damping
modules, the secondary vibrations, which act in another, than
axial, direction, are also actively damped. With a third actuator
or a damping module, which is arranged outside of the plane of the
first two actuators or damping modules, the vibrations in all of
the spacial directions are actively damped.
[0020] Advantageously, the mass of the hammer module is made as
large as possible and, in particular, larger than the other modules
or units, which permits to increase the power of the hand-held
power tool.
[0021] Advantageously, the side additional handle is also damped,
with the additional handle being rigidly connected with the handle
by a handle U-shaped housing part vibrations of which are actively
damped.
[0022] Advantageously, other, conventional means for a passive
reduction of vibrations applied to the handle, such as viscoelastic
material which are, used for attachment and/or during formation of
the handle, is combined with the active damping means according to
the present invention. As a result, additional particular vibration
or oscillation frequencies above the actively damped frequency
spectrum are damped.
[0023] Advantageously, the control circuit, which is formed of
sensors, microprocessor, and actuator, is designed for active
control or regulation in the region of from 10 to 100 Hz,
preferably, in the region of from 2 to 400 Hz, at a sampling time
of less than 1 ms, advantageously, less than 200 us.
[0024] Advantageously, the control circuit is based on one of the
following control principle: feedforward, feedback, or mixed
principle, preferably, with a feedback.
[0025] a) When a feedback principle is used, the acceleration of
the handle is measured with PT-1 controller (proportional low-pass
controller) and is transmitted back to the actuators as a control
voltage by a phase-changing member. The object of the control is
obtaining of mill-set value for the acceleration. The circuit can
be formed with one or two sensors.
[0026] b) Feedback of the tool acceleration and the
counter-electromotive force (EMF).
[0027] As it advantageous to place the sensor on an electronic
plate mounted on the tool, with this embodiment, an inverse
induction that takes place in the actuator during a relative
movement of the coil with respect to the magnet, is used. This
inverse induction can be calculated from the ratio of the current
to the voltage and from the actuator parameters (inductance and
resistance). As in the idle position of the handle, this relative
movement is determined only by the tool movement, and is again
calculated by integration based on an available acceleration data,
the inverse induction can be controlled proportionally to the tool
speed.
[0028] c) Feedforward of the tool acceleration
[0029] In case when a very small friction or a constant friction
occurs in bearing means, it is advantageous to use a feedforward
control. This is because the measurable tool acceleration produces
always the same action on the handle mass which can be compensated
by a feedforward control circuit. The advantage of the feedforward
control consists in that a reliable stability can be obtained which
cannot be insured by the feedback control circuit.
[0030] d) Feedback with distance information
[0031] With this control, the distance between non-interacting
masses is measured and is transformed into a control voltage by the
feedback control circuit.
[0032] e) Feedback of the force between the handle and the tool
[0033] Alternatively to the handle acceleration, according to an
advantageous embodiment, the force applied to the handle is
measured and by using a high-pass filter in controlled to 0 to keep
the handle in a constant position.
[0034] The novel features of the present invention, which are
considered as characteristic for the invention, are set forth in
the appended claims. The invention itself, however, both as to its
construction and its mode of operation, together with additional
advantages and objects thereof, will be best understood from the
following detailed description of preferred embodiment, when read
with reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] In the Drawings:
[0036] FIG. 1 shows a principle layout of an electrical percussion,
handheld power tool with an active vibration damping according to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0037] An electrical hand-held power tool 1 according to the
present invention, which is shown in the drawing and percussively
oscillates along a percussion axis A, is provided with means for
actively damping the vibrations of a handle 2 to which a press-on
force F is applied. The vibration damping means is supported for a
limited displacement along the percussion axis A with respect to an
oscillating hammer mechanism module 3 having a pneumatic,
eccentrically driven hammer mechanism and a driving motor 4.
[0038] The vibration damping means is arranged between the handle 2
and the oscillating hammer mechanism module 3 and includes two
electromechnical actuators 5a, 5b which operate in compression and
tension regions. The actuator 5a, 5b are arranged in a plane of the
handle 2, parallel to the percussion axis A, and are spaced from
each other along a line extending perpendicular to the percussion
axis A. The actuators 5a, 5b are formed as oscillation coils and
are connected with a microprocessor 7 by a driver 6. There are
further provided two, non-dumped, elastic springs 8a, 8b which
surround respective actuators 5a, 5b. The springs 8a, 8b are formed
as helical springs and form, together with respective actuators 5a,
5b, two damping modules. An auxiliary handle 9 is fixidly connected
with the handle 2 by a handle cup-shaped housing part 10. A sensor
11, which is formed as an acceleration pick-up, is provided in the
housing part 10. The sensor 11 is operationally connected with the
microprocessor 7 for transmitting signals thereto. Both, the
auxiliary handle 9 and the handle 2 are covered additionally with a
passive, viscoelastic outer damping layer 12.
[0039] Though the present invention was shown and described with
references to the preferred embodiment, such is merely illustrative
of the present invention and is not to be construed as a limitation
thereof, and various modifications to the present invention will be
apparent to those skilled in the art. It is, therefore, not
intended that the present invention be limited to the disclosed
embodiment or details thereof, and the present invention includes
all of variations and/or alternative embodiments within the spirit
and scope of the present invention as defined by the appended
claims.
* * * * *